Скачать или смотреть How to Efficiently Change Data in SQL Tables using Join Queries

A step-by-step guide on updating data in one SQL table based on another. Learn how to use join queries effectively!
---
This video is based on the question https://stackoverflow.com/q/69361735/ asked by the user 'Artur Dino' ( https://stackoverflow.com/u/16979302/ ) and on the answer https://stackoverflow.com/a/69361882/ provided by the user 'Hamed Naeemaei' ( https://stackoverflow.com/u/1998051/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: How to change data in table using data from 2 tables SQL query

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
How to Efficiently Change Data in SQL Tables using Join Queries

Updating data in SQL can sometimes be a complex task, especially when you're working with multiple tables. If you've ever faced a scenario where you need to update a row in one table based on values from another, you're not alone. In this guide, we'll discuss a common problem where you want to change a user's status based on their name, and we’ll walk through the solution step by step.

The Challenge: Updating User Status

You may have two tables:

users: This table contains the following columns:

id

first_name

last_name

user_workplace: This one consists of:

id

user_id (a foreign key referencing users.id)

status (which can be either DISABLED or ACTIVE)

The goal is to update the status in the user_workplace table to "DISABLED" based on the user's first and last name. This may sound straightforward, but it can get tricky when you're dealing with SQL joins.

Analyzing Previous Attempts

Common Mistakes

In your initial attempts to execute the SQL update, you encountered some issues:

Error Message: You received an error stating, "missing FROM-clause entry for table users," which often indicates a syntax error or a misunderstanding in how SQL joins work.

No Rows Updated: In another attempt, your query resulted in an "UPDATE 0" output, indicating that no rows were affected – meaning the query did not find any matching records.

The Solution: Using a Proper SQL Query

To successfully update the user's status, you need to correctly structure your UPDATE statement with a FROM clause that includes the necessary join. Here's the correct way to format your query:

[[See Video to Reveal this Text or Code Snippet]]

Breakdown of the Query

UPDATE Clause: This specifies which table you're updating (user_workplace).

SET Clause: Informs SQL that you want to change the status column to 'DISABLED'.

FROM Clause: This is where you specify the users table, which provides the context for your join.

WHERE Clause: Here, you apply conditions to ensure that only those records get updated where:

The user_id in user_workplace matches the id in users.

The first_name matches 'John' and the last_name matches 'Doe'.

Important Notes

Ensure that the names ("John" and "Doe") exactly match the corresponding entries in the database, including spaces.

It is also a good practice to consider case sensitivity in your queries, depending on your SQL database configurations.

Conclusion

By using a properly structured SQL query with the FROM clause, you can effectively update data in one table based on the criteria derived from another table. With practice, your SQL skills will improve, and these kinds of queries will become second nature.

If you're still having trouble with SQL queries or have any questions, feel free to leave a comment. Happy querying!